Discovery of Big Bang's Gravitational Waves Goes Bust, Due to Dust

A leaked analysis suggests that findings of gravitational waves from the big bang were illusory.

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The BICEP2 telescope (foreground) in Antarctica, shown with the South Pole Telescope, was the first to collect evidence of gravitational waves, a result now in question.

Photograph courtesy Steffen Richter, Harvard University

Back to the drawing board for how the big bang first went bang. Intergalactic dust has doomed last year's celebrated observations of gravitational ripples from the first moments of creation, according to astrophysics results leaked on Friday.

The BICEP2 scientific team announced evidence last March that surprisingly strong gravitational waves rippled through the big bang's fiery aftermath, called the cosmic microwave background. That seemed to confirm that the cosmos grew to a stunningly vast size in its very first moments some 13.8 billion years ago.

But the Friday leak of the European Space Agency's Planck satellite report, made in collaboration with the BICEP2 team, suggests that the signal was essentially an optical illusion. Intervening, obscuring dust lingering in our own galaxy, which emits near-infrared light of the same character as the cosmic microwave background, seems to have confounded the observation. (See "Big Bang Discovery Comes Under Fire.")

"It turns out that the fraction due to dust had been significantly underestimated," says the French Planck team's summary, in translation. "Once the fraction [of the signal] due to galactic [dust] emissions has been correctly subtracted, an excess remains, but at present it is too weak to be considered a detection."

Adding to results from an experiment at a related observatory, the Keck Array, the collaboration's summary suggests that the gravitational wave result might have been entirely due to "experimental noise."

"To be blunt, therefore, the BICEP2 measurement is a null result for primordial gravitational waves," says astrophysicist Peter Coles of the U.K.'s University of Sussex on his In the Dark blog. "It's by no means a proof that there are no gravitational waves at all, but it isn't a detection."

The BICEP2 results were seen as confirming cosmological "inflation" as an explanation for the rapid expansion of the universe in its first moments nearly 14 billion years ago.

Twice as strong as expected, the signal of gravitational waves imprinted on the cosmological microwave background, leftover heat from the big bang, suggested that cosmological inflation unfolded in a surprisingly simple manner.

News that the discovery team had relied to some extent on assumptions about galactic dust, rather than on Planck measurements, added to skepticism. The latest turn in the BICEP2 saga will likely lead to more criticism of "science by press conference."

The new report doesn't mean that cosmological inflation is wrong. That idea describes how conditions in the early universe would create strongly repulsive forces that stretch its boundaries exponentially to great distances. But it suggests the phenomena was less strong and more complex than the BICEP2 results implied. (For more on cosmological inflation, click here.)

What's Next

This year the BICEP2 team will start making measurements from an improved Antarctic observatory, which surveys a small portion of the sky looking for gravitational wave signals. A number of other teams are looking for these signals with methods unaffected by galactic dust.

And the Planck team is expected to make more gravitational wave measurements on its own in coming years.

As astrophysicist Coles remarks on his blog, "The search goes on..."

Correction: Peter Coles name was originally misspelled and has been corrected.